Recently, the need for toner suitable for high-speed printing, particularly toner capable of improving image quality and preventing hot offset has increased in the printing industry. “Hot offset” is a phenomenon in which some toner melted on a printing paper adheres to a fixing device after passing through the fixing device in the case where excessive amounts of toner are melted when the toner is heated while passing through the fixing device.
Thus, a toner having anti-hot offset properties is required.
Japanese Patent Publication No. 2001-117268 discloses a toner having binder resin particles that contain crystalline polyester with a cross-linking structure formed with unsaturated portions as main components and having spherical shape, and a method of preparing the toner. However, it is difficult to provide a large fixing temperature range using the toner.
Meanwhile, when a pulverization method is used to improve anti-hot offset properties, a resin cannot be used efficiently, and even when a polymer having a high molecular weight or a cross-linking structure is used, it is difficult to obtain sufficient performance. Also, since the pulverization method is used, it is difficult to control the shape of the toner particles; in particular, it is difficult to obtain spherical toner particles. Also, it is difficult to obtain toner particles with small diameters, which is required for high image quality.
Japanese Patent Publication No. 2006-038915 discloses a method of preparing a toner for solving the above-described problem relating to the pulverization method, wherein the method includes preparing a water suspension of polyester resin, adding a dispersion stabilizer to the water suspension, and adding an aqueous electrolyte solution in the presence of the dispersion stabilizer, thereby precipitating fine particles of a polyester resin in a form of coalescence. The polyester resin used in this method is a mixture of a cross-linked type polyester resin formed by using 60 mol % or more of propylene glycol with respect to a total alcohol component, and a straight chain type polyester resin. However, it is still difficult to provide a sufficient fixing temperature range using the toner prepared in this manner.